Washington: The United States’ freight rail sector has quietly become one of the nation’s largest sources of air pollution, now emitting more nitrogen oxide (NOx) a key contributor to smog and respiratory illnesses than all of the country’s coal-fired power plants combined. According to a Reuters analysis of government and industry data, in 2024 U.S. railroads released roughly 485,000 tons of NOx, exceeding the 452,000 tons generated by coal power facilities. The findings underscore a growing environmental challenge tied to an aging locomotive fleet and slow modernization.
Environmental advocates and public health experts have expressed alarm at the trend, noting that while coal has long been considered a major polluter, rail emissions have quietly overtaken it due to decades of deferred upgrades and regulatory leniency. Unlike trucks and passenger vehicles, freight locomotives face limited emissions oversight, allowing high-polluting engines to remain in service for decades.
The BNSF Railway, part of Warren Buffett’s Berkshire Hathaway, is the largest contributor, responsible for approximately one-third of total rail NOx emissions, or 161,500 tons. Analysts say the surge stems from the average freight locomotive being nearly 28 years old, with only a small fraction of the fleet meeting the newest environmental standards. Despite the availability of cleaner “Tier 4” engines, adoption has been slow, with BNSF’s modern units accounting for just 5% of its total locomotives.
The environmental impact is not theoretical. According to U.S. Environmental Protection Agency data, locomotive pollution contributes to an estimated $48 billion in health costs annually, including roughly 3,100 premature deaths linked to respiratory and cardiovascular diseases. Communities near major rail corridors face elevated exposure, amplifying concerns over public health and environmental justice.
Rail industry representatives defend their practices, emphasizing that rail remains the most fuel-efficient mode of long-distance freight transport. A single locomotive can move a ton of freight nearly 500 miles on one gallon of fuel, making it far more efficient than trucking. Industry groups argue that comparing locomotive emissions with coal plants overlooks the structural differences, including the ability of power generators to switch to lower-emission energy sources.
Regulatory and technological challenges continue to slow progress. Efforts to impose stricter clean air standards, including zero-emission locomotive rules in California, have faced resistance due to cost concerns and uncertainties about long-term policy support. Emerging alternatives such as hydrogen fuel cells, battery-electric engines, and biofuels show promise but remain constrained by range, performance, and infrastructure limitations, particularly for long-haul freight operations.
Experts warn that without decisive action, emissions from freight rail could undermine broader U.S. climate and air quality goals. While attention has focused on decarbonizing electricity generation and passenger transportation, freight rail represents a critical blind spot in achieving sustainable environmental outcomes. As global freight demand continues to grow, transitioning to cleaner locomotives is increasingly seen as essential to protecting public health and meeting climate commitments.